Viologen-Basedionic Polymer Binder, and Preparation Method and Use Thereof

This patent application claims the benefit and priority of Chinese Patent Application No 2024108277393 entitled “Viologen-based ionic polymer binder, and preparation method and use thereof” filed on Jun. 24, 2024, the disclosure of which is incorporated by reference herein in its entirety as part of the present application.

The present disclosure relates to the technical field of lithium-ion batteries, and in particular to a viologen-based ionic polymer binder, and a preparation method and use thereof.

In cathodes of lithium-ion batteries, a binder is to bond the active materials and conductive additives onto the current collector to form stable cathodes and then maintain integrity of the cathodes during charging and discharging process. The binder shows a significant impact on the battery performances. When the binder exhibits poor adhesion, the active materials and conductive additives may fall off, causing battery failure; when the binder exhibits poor electrochemical stability, the binder may undergo irreversible chemical reactions with lithium ions, resulting in a decrease in battery capacity. Therefore, it is highly needed to design high-performance binders to solve problems such as active materials shedding from current collector and low recycling performance.

At present, the common binder for cathodes of lithium-ion batteries is polyvinylidene fluoride (PVDF). However, the PVDF exhibits several defects. For example, the interaction between PVDF and active materials through van der Waals forces is weak, which leads to poor adhesion of active materials and conductive additives onto the current collector. Besides, PVDF is nonconductive for electron/lithium ion, which is not helpful for Litransportation and therefore leads to high polarization especially at high charge/discharge current density. Furthermore, the interface impedance is relatively high when using PVDF as a cathode binder. In order to overcome these problems existing in PVDF binders, there have been many studies on cathode/anode binders for lithium-ion batteries. For example, CN111180733A discloses a binder containing ethylene carbonate, which endows the polymer binder with certain elasticity. However, the cathode prepared by this polymer binder still has poor adhesion, leading to capacity retention of the battery not more than 70%. For another example, CN111635478A discloses a low-impedance binder containing an ionic liquid structural unit. This binder shows excellent ion transportation. When the cathodes prepared by employing this binder are applied to a lithium-ion battery, the recycling performance of lithium-ion battery at low charge/discharge current density is improved. However, the lithium-ion battery has poor capacity retention and recycling stability at high charge/discharge current density.

As a result, it has become a technical challenge that needs to be solved urgently in the technical field of lithium-ion batteries to design polymer binders with enhanced adhesion performance and suitable electrochemical properties to keep high capacity retention and good recycling stability of lithium-ion batteries at high charge/discharge current density.

An object of the present disclosure is to provide a viologen-based ionic polymer binder, and a preparation method and use thereof. In the present disclosure, the viologen-based ionic polymer binder exhibits excellent capacity retention and recycling stability under high-rate charge and discharge conditions.

To achieve the above object, the present disclosure provides the following technical solutions:

The present disclosure provides a viologen-based ionic polymer binder, having a chemical structure shown in formula I.

In some embodiments, the viologen-based acrylate is prepared by a process including the following steps:

In some embodiments, in step (1), the alkylating agent is at least one selected from the group consisting of methyl iodide, dimethyl sulfate (DMS), dimethyl carbonate (DMC), ethyl iodide, diethyl sulfate (DES), diethyl carbonate (DEC), propyl iodide, dipropyl sulfate (DPS), and dipropyl carbonate (DPC); the second solvent is at least one selected from the group consisting of dichloroethane (DCE), tetrahydrofuran (THF), dichloromethane (DCM), toluene, and chloroform; and the first alkylation reaction is conducted at a temperature of 10° C. to 35° C. for 1 h to 24 h.

In some embodiments, in step (2), the 1-halogeno alkan-1′-ol is at least one selected from the group consisting of 2-bromoethanol, 2-chloroethanol, 3-bromo-1-propanol, 3-chloro-1-propanol, 4-bromo-1-butanol, 4-chloro-1-butanol, 5-bromo-1-pentanol, 5-chloro-1-pentanol, 6-bromo-1-hexanol, 6-chloro-1-hexanol, 7-bromo-1-heptanol, 7-chloro-1-heptanol, 8-bromo-1-octanol, and 8-chloro-1-octanol; the third solvent is at least one selected from the group consisting of acetonitrile, N-methylpyrrolidone (NMP), N,N-dimethylformamide (DMF), and dimethyl sulfoxide (DMSO); and the second alkylation reaction is conducted at a temperature of 50° C. to 100° C. for 30 h to 72 h.

In some embodiments, in step (3), the salt containing the anion different from that of the 1-(hydroxyalkyl)-1′-alkyl viologen salt (1) is at least one selected from the group consisting of KPF, NaPF, NHPF, NaBF, KBF, NaBr, KBr, NaI, KI, NaSO, NaCO, KCO, CHSONa, CFSONa, and (CFSO)NLi; the fourth solvent is at least one selected from the group of deionized water, ethanol, NMP, DMF, and DMSO; and the ion exchange reaction is conducted at a temperature of 10° C. to 35° C. for 1 h to 12 h.

In some embodiments, in step (4), the vinyl carbonyl compound is at least one selected from the group consisting of 2-isocyanatoethyl acrylate, isocyanatoethyl methacrylate, acrylic acid, methacrylic acid, acryloyl chloride, and methacryloyl chloride; the catalyst is at least one selected from the group consisting of dibutyltin dilaurate (DBTDL), triethylamine (TEA), sodium carbonate, and potassium carbonate; the polymerization inhibitor is at least one selected from the group consisting of p-methoxyphenol, p-benzoquinone, and p-hydroquinone; the fifth solvent is at least one selected from the group consisting of NMP, DMF, THF, 1,4-dioxane, acetonitrile, and chloroform; and the esterification reaction is conducted at a temperature of 10° C. to 35° C. for 1 h to 36 h.

In some embodiments, the initiator for the free radical polymerization is at least one selected from the group consisting of azobisisobutyronitrile (AIBN), 1,1′-azobis(cyclohexane-1-carbonitrile) (ACCN), dimethyl 2,2′-azobisisobutyrate, and dibenzoyl peroxide (BPO); the first solvent is at least one selected from the group consisting of acetonitrile, toluene, acetone, NMP, DMF, THF, 1,4-dioxane, and chloroform; and the free radical polymerization is conducted at a temperature of 50° C. to 80° C. for 8 h to 12 h.

The present disclosure further provides use of the viologen-based ionic polymer binder as described in the above technical solutions or the viologen-based ionic polymer binder prepared by the method as described in the above technical solutions in preparation of an electrode of a lithium-ion battery.

In some embodiments, the electrode of the lithium-ion battery is one selected from the group consisting of a cathode and an anode.

In the present disclosure, the viologen-based ionic polymer binder is a polymer prepared from a viologen-based acrylate, at least one of an acrylate and poly(ethylene glycol) methyl ether acrylate. When the binder is used to prepare a cathode of a lithium-ion battery, the chain segment of the viologen-based acrylate acts as follows: first, quaternary ammonium cations and counter anions in a viologen structure are combined with cathode active materials of the lithium-ion battery through electrostatic interaction, which could enhance the adhesion between the cathode active materials. Second, the counter anions in the viologen structure could promote the transportation of lithium ions. Third, the viologen has a stable structure and reversible redox properties. When the ionic polymer is used as a binder for cathode of a lithium-ion battery, it is beneficial to improve the capacity retention and recycling stability of the lithium-ion battery. The chain segment of the polyacrylate could not only improve the flexibility of the binder and soften the electrode, but also could enhance the hydrophobicity of the binder, thereby avoiding the decrease in battery capacity and recycling performance caused by the absorbed water. On the one hand, the chain segment of the poly(ethylene glycol) methyl ether acrylate could enhance the flexibility of the binder; on the other hand, due to desirable lithium ion transportation, the chain segment(s) could improve the ion transportation between the cathode and the electrolyte interface and reduce the interface impedance. Therefore, a lithium-ion battery assembled with the cathode prepared by the viologen-based ionic polymer binder according to the present disclosure has lower interface impedance, higher specific capacity, higher capacity retention, and desirable recycling stability. The results of examples show that the viologen-based ionic polymer binder has a glass transition temperature of −45.3° C. to −24.5° C. A cathode prepared with the viologen-based ionic polymer binder has a peel strength of 120.1-145.7 N·m. A lithium iron phosphate|metal lithium battery assembled with the cathode prepared with the viologen-based ionic polymer binder has an initial discharge capacity of 141.5-145.2 mAh·gwith a cut-off voltage of 2.5 V to 4.2 V and a rate of 0.5C. The battery after 400 cycles has a discharge specific capacity of 128.5-136.3 mAh·g, showing a capacity retention of 89.17% to 93.87%. The lithium iron phosphate|metal lithium battery assembled with the cathode prepared from the viologen-based ionic polymer binder has an initial interface impedance of 204.1Ω to 211.9Ω.

In this text, m, n, and q separately represent mole fractions of corresponding repeating units in a polymer main chain with the proviso that a sum of m, n, and q is 100% (that is to say, m+n+q=1).

The present disclosure provides a viologen-based ionic polymer binder, having a chemical structure shown in formula I.

In some embodiments of the present disclosure, the alkyl is Cto Calkyl, and preferably methyl, ethyl, or butyl. In some embodiments, Ris ethyl or butyl. In some embodiments, Ris methyl. p is an integer in a range of 0 to 40, preferably 9 to 30, and even more preferably 9, 10, 12, 15, 20, or 30. In some embodiments, m is in a range of 0 to 0.9, preferably 0, 0.62, 0.68, 0.81, 0.86, or 0.9. In some embodiments, n is in a range of 0 to 0.75, preferably 0, 0.05, 0.16, 0.65, or 0.75. In some embodiments, q is in a range of 0.10 to 1, preferably 0.1, 0.14, 0.16, 0.22, 0.25, 0.35, or 1. The viologen-based ionic polymer binder having a structure shown in formula I according to the present disclosure could not only make the binder have good adhesion but also promote the transportation of lithium ions, thereby improving the capacity retention and recycling stability of the battery.

The present disclosure further provides a method for preparing the viologen-based ionic polymer binder, including the following steps: mixing a viologen-based acrylate, at least one of an acrylate and poly(ethylene glycol) methyl ether acrylate, an initiator, and a first solvent, and subjecting a resulting mixture to free radical polymerization to obtain the viologen-based ionic polymer binder; wherein

In the present disclosure, unless otherwise specified, all materials used are commodities well known to those skilled in the art.

In some embodiments of the present disclosure, the viologen-based acrylate is prepared by a process including the following steps:

In some embodiments of the present disclosure, 4,4′-bipyridine, an alkylating agent, and a second solvent are mixed, and a resulting mixture is subjected to a first alkylation reaction to obtain an N-alkyl-4,4′-bipyridine salt.

In some embodiments of the present disclosure, the alkylating agent includes at least one of methyl iodide, DMS, DMC, ethyl iodide, DES, DEC, propyl iodide, DPS, and DPC. In the present disclosure, the alkylating agent defined above undergoes alkylation reaction with the 4,4′-bipyridine to form the N-alkyl-4,4′-bipyridine salt.

In some embodiments of the present disclosure, the second solvent includes at least one of DCE, THF, DCM, toluene, and chloroform. In the present disclosure, the above solvent shows desirable solubility for the 4,4′-bipyridine and the alkylating agent, and thus is more conducive to fulfill the first alkylation reaction.

In some embodiments of the present disclosure, a mass ratio of 4,4′-bipyridine, the alkylating agent, and the second solvent is in a range of (160-250):(150-240):4000, preferably (190-240):(200-230):4000, and more preferably (195-235):(210-225):4000. The above mass ratio could avoid the formation of N,N-dialkyl-4,4′-bipyridine salt and is conducive to the formation of N-alkyl-4,4′-bipyridine salt.

In the present disclosure, there is no particular limitation on means for mixing 4,4′-bipyridine, the alkylating agent, and the second solvent, and any conventional mixing means may be used to fully dissolve the components. In some embodiments, 4,4′-bipyridine, the alkylating agent, and the second solvent are mixed under stirring.

In some embodiments of the present disclosure, the first alkylation reaction is conducted at a temperature of 10° C. to 35° C., preferably 15° C. to 30° C., and more preferably 20° C. to 30° C. In some embodiments, the first alkylation reaction is conducted for 1 h to 24 h, preferably 8 h to 20 h, and more preferably 10 h to 13 h. Controlling the temperature and time for the first alkylation reaction could avoid the formation of NN-dialkyl-4,4′-bipyridine salt and facilitate the formation of N-alkyl-4,4′-bipyridine salt.

In some embodiments of the present disclosure, a product obtained from the first alkylation reaction is mixed with a first precipitant, and a resulting mixture is subjected to filtration, followed by drying, to obtain the N-alkyl-4,4′-bipyridine salt.

In some embodiments of the present disclosure, the first precipitant is at least one of diethyl ether, n-hexane, and cyclohexane. In some embodiments, when the first precipitant is a mixture of two or more of the above, there is no special limitation on a ratio between the two or more, which may be mixed in any ratio. In the present disclosure, by using the first precipitant, the N-alkyl-4,4′-bipyridine salt could be separated from a reaction solution.

In some embodiments of the present disclosure, a mass ratio of the first precipitant to the product obtained from the first alkylation reaction is in a range of (4-11):1, and preferably (5-10):1. Controlling the amount of the first precipitant within the above range could fully precipitate the product obtained from the first alkylation reaction.

In the present disclosure, there is no particular limitation on operations of the filtering and drying, and operations well known to those skilled in the art may be used. In some embodiments, the drying is conducted at a temperature of 40° C. to 70° C., and preferably 50° C. to 60° C. In some embodiments, the drying is conducted for 8 h to 15 h, and preferably 10 h to 12 h.

In some embodiments of the present disclosure, after obtaining the N-alkyl-4,4′-bipyridine salt, the N-alkyl-4,4′-bipyridine salt is mixed with a 1-halogeno alkan-1′-ol and a third solvent, and a resulting mixture is subjected to a second alkylation reaction, to obtain a 1-(hydroxyalkyl)-1′-alkyl viologen salt (1).

In some embodiments of the present disclosure, the 1-halogeno alkan-1′-ol is at least one selected from the group consisting of 2-bromoethanol, 2-chloroethanol, 3-bromo-1-propanol, 3-chloro-1-propanol, 4-bromo-1-butanol, 4-chloro-1-butanol, 5-bromo-1-pentanol, 5-chloro-1-pentanol, 6-bromo-1-hexanol, 6-chloro-1-hexanol, 7-bromo-1-heptanol, 7-chloro-1-heptanol, 8-bromo-1-octanol, and 8-chloro-1-octanol. The above 1-halogeno alkan-1′-ol is selected to react with the N-alkyl-4,4′-bipyridine salt to form the 1-(hydroxyalkyl)-1′-alkyl viologen salt (1).

In some embodiments of the present disclosure, the third solvent is at least one selected from the group consisting of acetonitrile, NMP, DMF, and DMSO.

In some embodiments of the present disclosure, a mass ratio of the N-alkyl-4,4′-bipyridine salt, 1-halogeno alkan-1′-ol, and the third solvent is in a range of (390-420):(190-230):4000, and preferably (390-410):(195-230):4000.

In the present disclosure, there is no particular limitation on the mixing of the N-alkyl-4,4′-bipyridine salt, the 1-halogeno alkan-1′-ol, and the third solvent, and conventional mixing methods may be used to fully dissolve the above components.

In some embodiments of the present disclosure, the second alkylation reaction is conducted at a temperature of 50° C. to 100° C., and preferably 70° C. to 90° C. In some embodiments, the second alkylation reaction is conducted for 12 h to 72 h, preferably 40 h to 65 h, and more preferably 50 h to 63 h.

In some embodiments of the present disclosure, a product obtained from the second alkylation reaction is mixed with a second precipitant, and a resulting mixture is subjected to filtration, followed by drying, to obtain the 1-(hydroxyalkyl)-1′-alkyl viologen salt (1).

In some embodiments of the present disclosure, the second precipitant is at least one of DCM, DCE, diethyl ether, and n-hexane. In some embodiments, when the second precipitant is a mixture of two or more of the above, there is no special limitation on a ratio between the two or more, which may be mixed in any ratio.

In some embodiments of the present disclosure, a mass ratio of the second precipitant to the product obtained from the second alkylation reaction is in a range of (4-11):1, and preferably (6-11):1. In the present disclosure, the filtration and drying means and parameters thereof are the same as those of the filtration and drying after the product obtained from the first alkylation reaction is mixed with the first precipitant in the above technical solutions, and will not be described in detail here.

In some embodiments of the present disclosure, after obtaining the 1-(hydroxyalkyl)-1′-alkyl viologen salt (1), the 1-(hydroxyalkyl)-1′-alkyl viologen salt (1) is mixed with a salt containing an anion different from that of the 1-(hydroxyalkyl)-1′-alkyl viologen salt (1) and a fourth solvent, and a resulting mixture is subjected to ion exchange reaction to obtain a 1-(hydroxyalkyl)-1′-alkyl viologen salt (2). In some embodiments, the salt containing the anion different from that of the 1-(hydroxyalkyl)-1′-alkyl viologen salt (1) is at least one selected from the group consisting of KPF, NaPF, NHPF, NaBF, KBF, NaBr, KBr, NaI, KI, NaSO, NaCO, KCO, CHSONa, CFSONa, and (CFSO)NHLi. In some embodiments, when the salt containing the anion different from that of the 1-(hydroxyalkyl)-1′-alkyl viologen salt (1) is a mixture of two or more of the above, there is no particular limitation on a ratio between the two or more, which may be mixed in any ratio. Selecting the above types of salt containing the anion different from that of the 1-(hydroxyalkyl)-1′-alkyl viologen salt (1) is more conducive to combining the anions with the quaternary ammonium cations of viologen through ion exchange reaction, thereby forming the 1-(hydroxyalkyl)-1′-alkyl viologen salt (2).

In some embodiments of the present disclosure, the fourth solvent is at least one selected from the group consisting of deionized water, ethanol, NMP, DMF, and DMSO. The above solvent shows desirable solubility for 1-(hydroxyalkyl)-1′-alkyl viologen salt (1) and the salt containing the anion different from that of the 1-(hydroxyalkyl)-1′-alkyl viologen salt (1), thus promoting the ion exchange reaction to proceed fully.

In some embodiments of the present disclosure, a mass ratio of the 1-(hydroxyalkyl)-1′-alkyl viologen salt (1), the salt containing the anion different from that of the 1-(hydroxyalkyl)-1′-alkyl viologen salt (1), and the fourth solvent is in a range of (540-700):(470-1000):5000, preferably (550-570):(500-900):5000. Controlling the mass ratio of the 1-(hydroxyalkyl)-1′-alkyl viologen salt (1), the salt containing the anion different from that of the 1-(hydroxyalkyl)-1′-alkyl viologen salt (1), and the fourth solvent within the above range is more conducive to undergoing the ion exchange reaction between the salt containing the anion different from that of the 1-(hydroxyalkyl)-1′-alkyl viologen salt (1) with the 1-(hydroxyalkyl)-1′-alkyl viologen salt (1).

In the present disclosure, there is no particular limitation on an operation of mixing the 1-(hydroxyalkyl)-1′-alkyl viologen salt (1), the salt containing the anion different from that of the 1-(hydroxyalkyl)-1′-alkyl viologen salt (1), and the fourth solvent, and a technical scheme for preparing a mixed material well known to those skilled in the art may be used.